We have them here in short supply, but one wish I have is a postage parcel arriving one day on my doorstep filled with albino sliders or any baby tortoise for that matter as they fetch $1000-2500USD here!
audobon field guide lists them in the mississippi valley from illinois to the gulf, they are obviously in many more places now, even other continents, due to irresponsible owners releasing pets.
i didnt say you couldnt find them and get them for pets under 4", i said the law simply states no turtles under 4" are to be sold as pets in the U.S. i know you can get them smaller, i have done it for most of the babies i have had. and the little signs a lot of places put on the tanks of small turtles that say "for scientific or educational purposes only" does not get them off the hook.